After arriving on the scene, first I established the scope of the problem and areas affected.
The noise did not happen if I reved up the engine rpm in park. so we can rule out a valve bearing or other engine problem.
It did not happen if I gunned it in reverse, and it did not happen in any forward gear if the car was already in motion.
It only happened when hard acceleration form full stop and it went away after the car was going 5mph and faster. If I accelerate very gradually from full stop by only tapping the accelerator, it did not happen.
I asked my son to hold the brake while in drive and step on accelerator while I watched for the engine to rock out of place. Sure enough there was more than an inch of movement of the engine, so I knew it was the motor mounts.
I then asked my son if he hit a deep pot hole or other obstacle at high speed and he admitted he did. Then I asked him if this grinding noise problem was noticed only after striking the pothole and he said yes.
I checked the front end shocks and struts and they are shot.
So, that is the problem when bad shocks are not replaced. The road shocks are absorbed then by the engine mounts, which they are not designed for.
Diagnosis: 2 or more engine mounts were damaged, so the engine is no longer fully secured to the chassis. The most pronounced rocking or movement of the engine occurred when accelerating forward from full stop. Since the vehicle is front wheel drive, the automatic transmission assembly moved out of position slightly as well, not much, but enough for front wheel drive axle components to rub on something and cause said grinding noise. After the car reached some motion forward, the engine and attached rocked back or settled back in place due to gravity and rubbing noise stopped.
Lessons learned: Replace shucks and struts at recommended intervals and avoid pot holes.